function  [irfmat,irfst]=PCL_Part_info_irf( H, varobs, M_, dr, irfpers,ii)
% sets up parameters and calls part-info kalman filter
% developed by G Perendia, July 2006 for implementation from notes by Prof. Joe Pearlman to 
% suit partial information RE solution in accordance with, and based on, the 
% Pearlman, Currie and Levine 1986 solution.
% 22/10/06 - Version 2 for new Riccati with 4 params instead 5 

% Copyright (C) 2001-20010 Dynare Team
%
% This file is part of Dynare.
%
% Dynare is free software: you can redistribute it and/or modify
% it under the terms of the GNU General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
%
% Dynare is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with Dynare.  If not, see <http://www.gnu.org/licenses/>.


% Recall that the state space is given by the 
% predetermined variables s(t-1), x(t-1) 
% and the jump variables x(t).
% The jump variables have dimension NETA
        
        
    OBS = ismember(varobs,M_.endo_names);
    
        G1=dr.PI_ghx;
        impact=dr.PI_ghu;
        nmat=dr.PI_nmat;
        CC=dr.PI_CC;
        NX=M_.exo_nbr; % no of exogenous varexo shock variables.
        FL_RANK=dr.PI_FL_RANK;
        NY=M_.endo_nbr;
        if isempty(OBS) 
            NOBS=NY;
            LL=eye(NY,NY);
        else %and if no obsevations specify OBS=[0] but this is not going to work properly
           NOBS=size(find(OBS),2);
           LL=zeros(NOBS,NY);
           for i=1:NOBS
               LL(i,OBS(i))=1;
           end
        end

        if exist( 'irfpers')==1
            if ~isempty(irfpers)
                if irfpers<=0, irfpers=20, end;
            else
                irfpers=20;
            end
         else
            irfpers=20;
        end      
            
        ss=size(G1,1);
        pd=ss-size(nmat,1);
        SDX=M_.Sigma_e^0.5; % =SD,not V-COV, of Exog shocks or M_.Sigma_e^0.5 num_exog x num_exog matrix
        if isempty(H)
            H=M_.H;
        end
        VV=H; % V-COV of observation errors.
        MM=impact*SDX; % R*(Q^0.5) in standard KF notation
        % observation vector indices
        % mapping to endogenous variables.

        L1=LL*dr.PI_TT1;
        L2=LL*dr.PI_TT2;
        
        MM1=MM(1:ss-FL_RANK,:);
        U11=MM1*MM1';
        % SDX
	
        U22=0;
        % determine K1 and K2 observation mapping matrices
        % This uses the fact that measurements are given by L1*s(t)+L2*x(t)
        % and s(t) is expressed in the dynamics as
        % H1*eps(t)+G11*s(t-1)+G12*x(t-1)+G13*x(t).  
        % Thus the observations o(t) can be written in the form
        % o(t)=K1*[eps(t)' s(t-1)' x(t-1)']' + K2*x(t) where
        % K1=[L1*H1 L1*G11 L1*G12] K2=L1*G13+L2
        
		G12=G1(NX+1:ss-2*FL_RANK,:);
		KK1=L1*G12;
        K1=KK1(:,1:ss-FL_RANK);
        K2=KK1(:,ss-FL_RANK+1:ss)+L2;

        %pre calculate time-invariant factors
        A11=G1(1:pd,1:pd);
        A22=G1(pd+1:end, pd+1:end);
        A12=G1(1:pd, pd+1:end);
        A21=G1(pd+1:end,1:pd);
        Lambda= nmat*A12+A22;
        %A11_A12Nmat= A11-A12*nmat % test 
        I_L=inv(Lambda);
        BB=A12*inv(A22);
        FF=K2*inv(A22);       
        QQ=BB*U22*BB' + U11;        
        UFT=U22*FF';
        % kf_param structure:
        AA=A11-BB*A21;
        CCCC=A11-A12*nmat; % F in new notation
        DD=K1-FF*A21; % H in new notation
        EE=K1-K2*nmat;
        RR=FF*UFT+VV;
        if ~any(RR) 
            % if zero add some dummy measurement err. variance-covariances 
            % with diagonals 0.000001. This would not be needed if we used
            % the slow solver, or the generalised eigenvalue approach, 
            % but these are both slower.
            RR=eye(size(RR,1))*1.0e-6;
        end
        SS=BB*UFT;
        VKLUFT=VV+K2*I_L*UFT;
        ALUFT=A12*I_L*UFT;
        FULKV=FF*U22*I_L'*K2'+VV;
        FUBT=FF*U22*BB';
        nmat=nmat;
        % initialise pshat
        AQDS=AA*QQ*DD'+SS;
        DQDR=DD*QQ*DD'+RR;
        I_DQDR=inv(DQDR);
        AQDQ=AQDS*I_DQDR;
        ff=AA-AQDQ*DD;
        hh=AA*QQ*AA'-AQDQ*AQDS';%*(DD*QQ*AA'+SS');
        rr=DD*QQ*DD'+RR;
        ZSIG0=disc_riccati_fast(ff,DD,rr,hh);
        PP=ZSIG0 +QQ;
        
        exo_names=M_.exo_names(M_.exo_names_orig_ord,:);

        DPDR=DD*PP*DD'+RR;
        I_DPDR=inv(DPDR);
        PDIDPDRD=PP*DD'*I_DPDR*DD;
        %GG=[CCCC (AA-CCCC)*(eye(ss-FL_RANK)-PP*DD'*I_DQDR*DD); zeros(ss-FL_RANK) AA*(eye(ss-FL_RANK)-PP*DD'*I_DQDR*DD)];
        GG=[CCCC (AA-CCCC)*(eye(ss-FL_RANK)-PDIDPDRD); zeros(ss-FL_RANK) AA*(eye(ss-FL_RANK)-PDIDPDRD)];
        imp=[impact(1:ss-FL_RANK,:); impact(1:ss-FL_RANK,:)];
        % Calculate IRFs of observable series
        %The extra term in leads to
        %LL0=[EE  (H-EE)(I-PH^T(HPH^T+V)^{-1}H)].
        %Then in the case of observing all variables without noise (V=0), this 
        % leads to LL0=[EE  0]. 
        I_PD=(eye(ss-FL_RANK)-PDIDPDRD);
        LL0=[ EE (DD-EE)*I_PD];
        %OVV = [ zeros( size(dr.PI_TT1,1), NX ) dr.PI_TT1 dr.PI_TT2];
        VV = [  dr.PI_TT1 dr.PI_TT2];
        stderr=diag(M_.Sigma_e^0.5);        
            irfmat=zeros(size(dr.PI_TT1 ,1),irfpers);
            irfst=zeros(size(GG,1),irfpers); 
            irfst(:,1)=stderr(ii)*imp(:,ii);
            for jj=2:irfpers;
                irfst(:,jj)=GG*irfst(:,jj-1); % xjj=f irfstjj-2
                irfmat(:,jj-1)=VV*irfst(NX+1:ss-FL_RANK,jj);
                %irfmat(:,jj)=LL0*irfst(:,jj);  
            end   
            save ([M_.fname '_PCL_PtInfoIRFs_' num2str(ii) '_' deblank(exo_names(ii,:))], 'irfmat','irfst');